Upgrade RAM on Apple Retina iMac 5K (Late 2015) / How To install memory - YouTube
27 inch iMac with Retina 5k Display 2019 3.7GHz i5 2TB Fusion Drive 16GB RAM | Refurbished | Techable
Adamanta 16GB (1x16GB) Memory Upgrade for 2020 Apple iMac 27" w/Retina 5K Display, 2019 Apple iMac 27" w/Retina 5K Display, 2018 Apple Mac Mini DDR4 2666Mhz PC4-21300 SODIMM 2Rx8 CL19 1.2v DRAM
Memory Upgrades for 2019-2020 iMac 27-Inch - Up to 128GB
How to upgrade RAM in the (Mid 2017) 5K iMac and save up to ~$900 [Video] - 9to5Mac
End of life Sale] Apple 27" iMac with Retina 5K Display; 3.3 GHz Intel Core i5 Quad Core, 8GB RAM, 2TB Fusion Drive, AMD Radeon R9 M395 2GB, (Late 2015) For $1399
Apple iMac with 5K Retina display (27-inch) review: Apple's 5K iMac impresses expert eyes (review) - CNET